Phosphorus management strategies for corn and soybean in the Upper US Midwest

It has been questioned whether the sufficient phosphorus (P)management approach could maximize potential grain yield in today's agricultural systems. The objective of this research was to establish six long-term experiments across Minnesota to test phosphorus (P) management strategies on soils with a defined long-term P history. Four soil test phosphorus (STP) interpretation classes were established as whole plots (low, medium, high, and very high). Split-plots within each STP class consisted of one split-plot that did not receive P (−P), and the second split-plot received a broadcast application of P fertilizer (+P) at the rate of 73 (low), 44 (medium), 15 (high), and 15 (very high) kg P ha⁻¹. Grain yield, grain P concentration, and grain P removal were determined during corn (Zea mays L.) (2015 and 2016) and soybean [Glycine max (L) Merr.] (2017) growing seasons. Grain yield was increased by P fertilizer at 7 of 18 site-years. Grain yields were similar between fertilized STP plots at the very low and low for corn and very low for soybean compared to nonfertilized or fertilized high and very high STP plots. No yield increase was noted for fertilized high or very high plots. Grain P removal was increased by applied P at 14 of 18 site-years at the low and medium STP classes with no increase for the high and very high P testing soils. Results from this research indicate no greater yield potential for soils built to high or very high STP classes versus adequately fertilizing low- or medium-testing soils.